1. Field of the Invention
The present invention relates to a microflow cell and, more particularly, to the improvement of a micro flow cell for analyzing the sample in the cell by an optional means.
2. Description of the Prior Art
Microflow cells are now used in various fields of analysis and separation.
For example, in capillary electrophoresis (CE), a capillary tube having an inner diameter of about 50 .mu.m is used, and a part of the capillary (fused silica) tube can be used as a flow cell. In order to analyze the sample in the flow cell, an ultraviolet light (UV) absorbance detector is widely used by virtue of its simple structure.
Use of a fluorescence detector for the analysis of the sample in the capillary tube has been groped. Although the method of adopting fluorescence detection enables the analysis with higher selecting and sensitivity, very few reports has hitherto been made on this method.
This is ascribed to the fact that since a general capillary electrophoresis tube has an inner diameter of not more than 50 .mu.m, a small cell corresponding to the tube is required.
That is, the intensity of the scatted light of the excitation light by the flow cell becomes so high as to inconveniently raise the level of the background signal and the noise.
Several methods have been proposed to solve this problem. For example, Green and his co-worker and Cheng and his co-worker use a sheathed cuvette flow chamber and Fernandez and his co-worker use a fluorescence microscope.
Among these, some practical reports have been made on laser-excited fluorescence detection. Kerr and Jeung suggest that indirect fluorescence detection is useful in capillary electrophoresis. Since a laser beam is suitable for focussing light beam and can be projected to the small inner diameter of a fused silica capillary in the form of a small spot, it is possible to suppress the increase in background signal and noise caused by scattered light.
However, use of a laser as a light exciting source for the fluorescence measurement of capillary electrophoresis has some problems. For example, it makes the continuous change of the exciting wavelength impossible, it involves a high cost and the laser has a large size in comparison with the capillary electrophoresis separation system itself.
If use of a general fluorescence detector for HPLC is possible, it is very convenient because change of exciting wavelength is easy. In addition, the cost of the detection mechanism is lower than that of the system using a microscope or a laser.
However, it is very difficult to obtain a projection spot of not more than 50 .mu.m by an incoherent light beam. It is also difficult to reduce the noise level caused by the scattering of the light exiting by a small flow cell.